Diseases of the glomerulus, the filtering unit of the kidney, account for over 60% of all cases of end-stage renal disease, a major health problem worldwide. Among them are diabetic nephropathy, Goodpasture (GP) syndrome and Alport syndrome, which affect the collagen IV network of the glomerular basement membrane. The five Specific aims target fundamental questions about collagen IV structure and assembly, and role in Goodpasture autoimmune disease. The overall goal is to gain insight, at the atomic level, into mechanisms of molecular recognition that underlie structure-function relationships. Aim 1: To Characterize the formation of sulfilimine bonds. We discovered a novel sulfilimine bond (S=N) between methionine and hydroxylysine in the NC1 domains of collagen IV. This bond stabilizes the networks and plays a key role in conferring immune privilege to immunogenic sites that become reactive in Goodpasture autoimmune disease. We hypothesize that S=N bond formation is catalyzed by an enzyme in the extracellular matrix. Aim 2: To determine mechanisms for chain-specific assembly of collagen IV networks via NC1 domain recognition modules. We have established that the NC1 domains play a key role as recognition modules. We hypothesize that the code for assembly resides primarily within two distinct NC1 motifs. Aim 3: To characterize the quaternary structure of the 7S domain of collagen IV networks. The 7S domain, located at the N-terminus of protomers is critical for the assembly of networks. It contains binding sites for usherin, a defective protein in Usher syndrome, for bacterial Dr adhesins in chronic pyelonephritis, and for integrins. We hypothesize that the quaternary structure of the 7S dodecamer is stabilized by both non-disulfide (sulfilimine and lysylaldehyde-derived crosslinks) and disulfide bonds.Aim 4: To characterize the heterogeneity of 13 GP and 15 GP autoantibodies. We have recently determined that the a5 Gp autoantibodies, in addition to the well-known a3 GP autoantibodies are pathogenic. The current knowledge about their molecular diversity and the structure of GP-autoantibody is very limited. We hypothesize that these pathogenic GP autoantibodies are clonally restricted (oligoclonal). Aim 5: To determine the molecular structure of complete GP neoepitopes in the 13NC1 monomer. We identified four homologous hotspot regions within 13NC1 and 15NC1 monomers, which are important for GP antibody binding. We hypothesis that complete epitopes for 13NC1-specific GP autoantibodies encompass the EA/EB regions and but extend outside of these regions and are formed upon the change in hexamer conformation. The achievement of these aims will result in novel insights into mechanisms that can serve as a platform for developing treatments against glomerulosclerosis in patients with GP syndrome, diabetes mellitus, and other glomerular diseases, thus positively affecting the quality of life for millions of people.